Lotus Elan

tach with pertronix

PostPost by: rdssdi » Fri Jan 08, 2016 7:07 pm

Years ago I had my tach upgraded. I added a Pertronix ignition. The tach did not function. I was told to run the power that was to go directly to the distributor to the tach then back to the distributor. Essentially making a large loop of the white/black wire. It worked. Although I was suspicious of the efficacy of this wiring as the car seemed to run marginally worse.

I recently worked on the voltage stabilizer and tach wiring. The car would not start. If I bypass the loop to the tach by wiring as "normal" the car starts up.

Is there a way of getting a signal to the tach with out placing the tach in series with the distributor trigger lead? A bad connection or tach problem will stop the engine or possibly make it run poorly.

I have no idea what electronic mods were done to the tach when it was upgraded. Is there a new tach which would fit and work without being in the distributor power loop?

Bob
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PostPost by: mbell » Fri Jan 08, 2016 7:33 pm

I run a pertronix on mine and the standard tach seem to be working ok for me, some people have to do a RVC/RVI conversion to get them to work accurately with electronic ignition.

I am not quite following how you have your wired up but I have the tach wired as standard and the additional 12V supply to the Pertronix unit powered from a separate switched 12v source and not from the +ve side of the coil.
'73 +2 130/5 RHD, now on the road and very slowly rolling though a "restoration"
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PostPost by: CG901 » Fri Jan 08, 2016 7:52 pm

I concur with mbell. I had the pertronix installed and the RVC/RVI board installed in the tach, with no problems at all. Car had been converted to neg ground by the PO.
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PostPost by: Grizzly » Fri Jan 08, 2016 10:14 pm

Just to add, once you have done the RVC/RVI conversion use a clean switched power to the Ignition module rather than as the instructions say to connect the power to the + side of the coil (creates interference which makes the rev counter do odd things when your driving)
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PostPost by: rdssdi » Fri Jan 08, 2016 10:27 pm

I must evaluate what the wiring in my car is. It is a 1969 Federal +2. I installed an Autosparks supplied custom wiring harness. Most of the wire color codes match the factory schematic.

If I run "clean" +12 to the Pertronix red wire and the other Pertronix black wire connecting to the opposite side (trigger) (white / block wire exiting loom at distributor) of the coil, where does the tach get its signal?

bob
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PostPost by: europatek » Fri Jan 08, 2016 11:13 pm

Interesting to read your comments about the engine performance with the Pertronix installed. I installed one in both my Elan and Cortina. The Cortina runs great and it's one of the best upgrades I've made. The Elan- not so. It runs worse and kind of super excites the engine. It won't idle properly and any carb issues are magnified. I went back to points and it's much better. My only thought is to take the positive feed directly from another source like the ignition switch or the solenoid to see if that makes a difference. The tacho worked fine in both.
From memory the standard tacho signal is from the white looped wire that runs from the ignition switch to the coil- the live feed that is to the coil.
I ended up upgrading the Cortina tacho and it now takes a signal directly from the negative side of the coil. I'll upgrade the Elan one day.
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PostPost by: ricarbo » Sat Jan 09, 2016 2:16 pm

Sounds a bit like the connection of the modified rev counter is placing a load on the Pertronix. In that case, I would connect the tach signal via a resistor. A value of 10k might be a good starting point (then try 1k and 100k).
Just a thought.
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PostPost by: rdssdi » Sat Jan 09, 2016 3:34 pm

I looked at the wiring. I wired the +12 (red wire) from the Pertronix to the +12 of the coil. I ran the trigger (-) lead from the wiring loom exiting at the distributor to the tach. The wire from the tach went to the Pertronix black (trigger) wire. This is what had been recommended. Quite a circuitous route for the signal to travel.

I now have the trigger (white/ black wire) directly from the loom to the distributor. Circumventing the tach. The engine runs.

I need to get a tach that will function with one wire going to the tach providing the signal from the trigger side instead of the tach being in the circuit as I had been advised and apparently is required for my current tach to function.

This may be accomplished with a new rebuild of the tach. I am reluctant to purchase a new Smiths (Caerbont) tach as it will not have the warning and turn signal lights. It may be possible to ad those to a new tach.

I will contact instrument companies to see what internal modifications they offer as well as their recommended wiring for the tach post conversion.

Any suggestions of companies in the U.S. who can provide this conversion?

Bob
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PostPost by: prezoom » Sat Jan 09, 2016 4:46 pm

I converted my S2 distributor to Pertronix eight years ago, when I changed from dynamo to alternator. Had a local instrument shop do the tach conversion from positive to negative. I connected the black wire from the Pertronix to the negative side of the coil and the red wire to the positive side. When first installed, the tach did not function. After some digging, I found that the white wire from the ignition, that passes through apparatus on the back of the tach needed to be reversed, changing the direction of current flow. Found this info in the back of a Moss Motors catalog. Everything has worked just find since, except when a ground wire came loose at the back of the tach, which caused a low rpm reading.
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PostPost by: Grizzly » Sat Jan 09, 2016 8:56 pm

rdssdi wrote:I must evaluate what the wiring in my car is. It is a 1969 Federal +2. I installed an Autosparks supplied custom wiring harness. Most of the wire color codes match the factory schematic.

If I run "clean" +12 to the Pertronix red wire and the other Pertronix black wire connecting to the opposite side (trigger) (white / block wire exiting loom at distributor) of the coil, where does the tach get its signal?

bob

When you fit the Pertronix wire it exactly how the points where fitted, the only difference is the module requires a 12v power supply where the Points don't, Don't connect that red wire to the Coil + side as the instructions suggest as the Collapsing field of the coil means the Ignition module doesn't get a clean 12v feed. Yes it will run but if your rev counter is old or you have an original RVC rev counter or early spiyda kit you will get some weird Rev counter issues as the signal going to it will have interference.
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PostPost by: rdssdi » Sat Jan 09, 2016 9:05 pm

I do not understand the difference between wiring the +12 for the Pertronix from the + 12 coil terminal or the ignition switch. It appears the +12 coil terminal is powered by the ignition switch.

I believe the Tach power is supplied from the loom at the tach. The tach uses the "trigger" wire White / black for the signal.

Bob
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PostPost by: mbell » Sat Jan 09, 2016 10:49 pm

rdssdi wrote:I do not understand the difference between wiring the +12 for the Pertronix from the + 12 coil terminal or the ignition switch. It appears the +12 coil terminal is powered by the ignition switch.


The standard tach works by sensing the current pulses sent to the coil that create the spark (one per spark). So the tach can work out the engine speed by the frequency of pulse divided by number cylinders. Hence why the tach is specific to number of engine cylinders.

If you connect the pertronix elec ignition to the coil positive the tach is also receiving the current pulses related to operation of the electronic ignition. In theory this is probably an extra current pulse per spark. Hence the tach often read 2x, but the current pulse will be quite small so might not always be picked up as a spark. Hence you get loads of weird tach bouncing and wrong readings.

If you connect the +ve supply for the electronic ignition to a circuit isolated from the tach it shouldn't pick up the current pulses for the electronic ignition and if your lucky you tach will just work the same as with points.
'73 +2 130/5 RHD, now on the road and very slowly rolling though a "restoration"
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PostPost by: stugilmour » Mon Jan 11, 2016 2:14 pm

rdssdi wrote:
Any suggestions of companies in the U.S. who can provide this conversion?

Bob


Bob, sorry for late reply. Did you get it sorted?

I got my tach converted at Nisonger Instruments, located in New York. They turned it around in about six weeks. The tach looks the same as stock (cleaned up a bit) and all of the warning lights stay the same. Also got the speedometer recalibrated. I recall speaking with them on the phone to confirm shipping details, cost, etc.

http://www.nisonger.com

Sort of confused a bit with your present wiring details, but the guys have covered off with good advice regarding separate power supply, etc. I would add I got my original tach to work with the Pertronix, but it was very difficult to adjust correctly and was therefore not particularly accurate. Eventually it quit reading correctly. The 50 year old components were probably just past their best. The rebuilt unit works fine, and is marked on the back of the case for wiring revisions.

HTH

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PostPost by: Grizzly » Tue Feb 02, 2016 12:38 pm

rdssdi wrote:I do not understand the difference between wiring the +12 for the Pertronix from the + 12 coil terminal or the ignition switch. It appears the +12 coil terminal is powered by the ignition switch.

I believe the Tach power is supplied from the loom at the tach. The tach uses the "trigger" wire White / black for the signal.

Bob


Ok, right. It's a bit difficult to explain but you know how a coil works (you put 12v across it and it builds up an Electro field until you remove the neg which releases the stored charge down the HT lead). The problem comes if you connect your Electric ignition 12v supply to the coil 12v, when the coil is doing its thing the electro magnetic field causes interference to the electronic ignition module (basically the 12v feed is not clean it has interference caused by the coil's magnetic field collapsing, you can see the bad signal if you hook up an oscilloscope)

On my car what i got was the Tacho getting confused, it would shoot over to red line when the engine was idling things like that. So to fix this i ran a fresh 12v power from the Ignition as far away from the coil as possible and fitted a small gizmo Spydr made for me to clean the Tacho's 12v signal (i believe the latest kits have this gizmo integrated link to my issues lotus-electrical-f38/odd-rev-counter-jumping-t33543-15.html)
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PostPost by: oddysseus » Fri Feb 26, 2016 5:30 pm

Hi,
This thread appeared just as i was about to start an overlapping one.
36/9368 has a Pertronix ignitor module fitted, and i have an intermittent problem which might be related to this discussion.
Occasionally i get what seems to be ignition failure. Not total, but enough to lose most power while running. If it happens while starting from cold i can fix it by running 12v to the coil.
A perusal of this forum led me to the conclusion that a possible intermittent failure point is the connection at the tach. Others have stated that power runs from the ignition switch to the tach, from where it continues to the coil. A poor connection at either tach terminal could cause my intermittent signal.
Some have stated that bridging the tach terminals solves the problem.
Before i go ahead and pull the dash, could anyone comment on this?
TIA,
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